1) Field of the Invention
The present invention relates to a self-supporting sheet-like structure containing a substrate layer and a structured coating on at least one surface of the substrate layer. The coating composition includes inert particles.
The invention furthermore relates to a process for the production of a sheet-like structure according to the invention, having a structured coating and a firmly adhering and abrasion-resistant structured coating on a polymer substrate. The coating being applied as an aerosol simultaneously with a corona treatment to the substrate layer.
2) Prior Art
In the case of sheet-like moldings of polymeric materials, such as films or sheets, inadequate slip and frictional properties during production and further processing of the materials lead to many undesirable problems. Static friction and sliding friction and blocking against one another and against guide or direction-changing elements, such as, for example, rollers, are examples of some of the undesirable problems.
A conventional suitable solution for solving this problem consists of incorporating in the material of the substrate layer inert particles which lead to a certain surface structure and thus have an advantageous effect on the sliding behavior of the molding. Examples of such inert particles, which can be incorporated either during the preparation of the thermoplastic or via a masterbatch during production of the molding, are inorganic natural or synthetic compounds, such as BaSO.sub.4, CaCO.sub.3, TiO.sub.2, SiO.sub.2, kaolin, Ca phosphates, etc., or organic particles, for example those consisting of crosslinked acrylates. The concentrations vary within wide limits, i.e., in the range from 0.001 to 1.0 percent by weight.
As already mentioned, a substantial improvement in the sliding properties of the moldings can be achieved by this solution, which also has an advantageous effect on the performance characteristics of the articles produced therefrom.
However, the disadvantage here is that the inert particles, before incorporation, have to be subjected to a very complicated, expensive treatment process for establishing the particle size distribution tailored to the particular surface roughness required and for incorporation into the matrix, in order to avoid other disadvantages, such as, for example, increased abrasion on contact with guide elements and the like. Furthermore, the optical properties of the substrates can also be adversely affected in some cases.
EP-A-O 153 853 describes a substrate film for a magnetic tape, the said film having a net-like coating which contains fine particles and is intended to impart the necessary frictional properties to the said substrate film. In this process, the coating materials, such as the colloidal silicates, have to be mixed with polymeric binders and the mixture applied to the surface of the substrate between the individual orientation steps. One of the disadvantages of this process is that the formation of the structures necessitates at least one stretching step, i.e., is linked with the process for the production of the film.